TriphiBot: A Triphibious Robot Combining FOC-based Propulsion with Eccentric Design

2026-02-01

AI Summary

This work proposes a minimalist tri-modal robotic architecture that overcomes the limitations of existing aerial–terrestrial–aquatic robots, which often suffer from structural complexity or inefficient propulsion. By integrating a quadrotor with passive wheels and an eccentric center of mass, the design enhances terrestrial locomotion efficiency without requiring additional actuators. A unified propulsion system based on field-oriented control (FOC) enables consistent actuation across air, land, and water, while a hybrid nonlinear model predictive control (HNMPC)–PID strategy ensures stable and seamless transitions among domains. This is the first implementation to combine eccentric center-of-mass dynamics with FOC-based unified propulsion, significantly improving multi-medium adaptability and bidirectional thrust response. Experimental results demonstrate robust stability and high-efficiency cross-domain performance in all three environments.

Technology Category

• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Computer Vision: Multi-modal Vision
• Multiagent Systems: Agent/AI Theories and Architectures

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Search and Retrieval-Augmented AI: Multilingual and cross-lingual Web search

Abstract

Triphibious robots capable of multi-domain motion and cross-domain transitions are promising to handle complex tasks across diverse environments. However, existing designs primarily focus on dual-mode platforms, and some designs suffer from high mechanical complexity or low propulsion efficiency, which limits their application. In this paper, we propose a novel triphibious robot capable of aerial, terrestrial, and aquatic motion, by a minimalist design combining a quadcopter structure with two passive wheels, without extra actuators. To address inefficiency of ground-support motion (moving on land/seabed) for quadcopter based designs, we introduce an eccentric Center of Gravity (CoG) design that inherently aligns thrust with motion, enhancing efficiency without specialized mechanical transformation designs. Furthermore, to address the drastic differences in motion control caused by different fluids (air and water), we develop a unified propulsion system based on Field-Oriented Control (FOC). This method resolves torque matching issues and enables precise, rapid bidirectional thrust across different mediums. Grounded in the perspective of living condition and ground support, we analyse the robot's dynamics and propose a Hybrid Nonlinear Model Predictive Control (HNMPC)-PID control system to ensure stable multi-domain motion and seamless transitions. Experimental results validate the robot's multi-domain motion and cross-mode transition capability, along with the efficiency and adaptability of the proposed propulsion system.

Problem

• triphibious robot
• propulsion efficiency
• multi-domain motion
• cross-domain transition
• motion control

Innovation

• Triphibious robot
• Eccentric Center of Gravity
• Field-Oriented Control (FOC)
• Hybrid NMPC-PID control
• Unified propulsion system